Labor has always played a significant role in Democratic politics, but rarely has it been called upon to do more than it will be asked to do this year.

Even though overall union membership has been declining in recent years, much of it remains concentrated in a number of battleground states, including Pennsylvania, Ohio and Michigan. All three states are must-wins for the Democratic nominee in a closely contested race. Labor is also making important inroads among working-class voters in new Democratic opportunity states such as New Mexico and Nevada.

The Democratic nominee will not carry white blue-collar workers as a group, but it is essential that the party’s standard-bearer keep the score down in this important demographic group. He cannot afford to lose white male blue-collar workers by wide margins and expect to carry battleground states. And he cannot assume he will be rescued solely by increased turnout among non-labor-affiliated African-Americans, young people and upper-income liberal whites. It takes at least four to tango in this particular dance.

That’s where organized labor comes into play.

In recent years, organized labor has done an excellent job convincing its membership to support Democratic candidates. Studies have shown that organized labor’s efforts directed at union households have increased support for Democratic candidates 15 percent to 20 percent, as compared with nonunion households. Labor is a credible messenger to its own members on issues such as jobs and health care.